While they won’t know the sex of the cub for another couple of weeks, they were able to take vital sign readings Sunday. The cub weighed 137 grams or 4.8 ounces, had good heart and lung sounds, and good signs for intestinal function.

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Mei Xiang was artificially inseminated twice March 30 after failing to breed naturally with the zoo's male panda Tian Tian. It's not clear who the proud father is: Mei Xiang was inseminated with previously frozen semen from both Tian Tian and Gao Gao, a panda at the San Diego Zoo.

Mei Xiang has given birth to two cubs in the past. A female cub, born last September, lived only six days. Her birth was a surprise; she had not shown up on any ultrasounds. An autopsy determined she may have been born prematurely. Mei Xiang's only surviving cub, Tai Shan, was born in 2005 and now lives in China.

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According to an agreement with the Chinese government, the cub will stay at the National Zoo for four years and will then be sent to China.